Various articles, including biomedical devices, are formed of organosilicon-containing materials. One class of organosilicon materials useful for biomedical devices, such as soft contact lenses, is silicon-containing hydrogel materials. A hydrogel is a hydrated, crosslinked polymeric system that contains water in an equilibrium state. Hydrogel contact lenses offer relatively high oxygen permeability as well as desirable biocompatibility and comfort. The inclusion of a silicon-containing material in the hydrogel formulation generally provides higher oxygen permeability since silicon based materials have higher oxygen permeability than water.
Another class of organosilicon materials is rigid, gas permeable materials used for hard contact lenses. Such materials are generally formed of silicon or fluorosilicon copolymers. These materials are oxygen permeable, and more rigid than the materials used for soft contact lenses. Organosilicon-containing materials useful for biomedical devices, including contact lenses, are disclosed in the following U.S. patents: U.S. Pat. No. 4,686,267 (Ellis et al.); U.S. Pat. No. 5,034,461 (Lai et al.); and U.S. Pat. No. 5,070,215 (Bambury et al.).
In addition, traditional siloxane-type monomers are hydrophobic and lenses made with them frequently require additional treatment to provide a hydrophilic surface. Although not wishing to be bound by a particular theory, the inventors believe that providing a charged siloxane-type random copolymer such as the quaternary siloxane-type random copolymers disclosed herein results in a hydrophilic siloxane-type random copolymer. It is believed that the hydrophilic quaternary groups interact with the electronegative portion of the polar water molecule.
Soft contact lens materials are made by polymerizing and crosslinking hydrophilic monomers such as 2-hydroxyethylmethyacrylate, N-vinyl-2-pyrrolidone, and combinations thereof. The polymers produced by polymerizing these hydrophilic monomers exhibit significant hydrophilic character themselves and are capable of absorbing a significant amount of water in their polymeric matrices. Due to their ability to absorb water, these polymers are often referred to as “hydrogels”. These hydrogels are optically clear and, due to their high levels of water of hydration, are particularly useful materials for making soft contact lenses. Siloxane-type monomers are well known to be poorly soluble in water as well as hydrophilic solvents and monomers and are therefore difficult to copolymerize and process using standard hydrogel techniques. Therefore, there is a need for new siloxane-type random copolymers that have improved solubility in the materials, specifically the diluents, used to make hydrogel lenses. Further there is a need for random copolymers that result in a polymerized medical device that is extractable in water instead of the organic solvents used in the prior art.
The present invention provides novel cationic organosilicon-containing random copolymers which are useful in articles such as biomedical devices including contact lenses.